After an oil or gas well has been drilled, it is necessary to introduce into the well a valve string so that the oil or gas may be removed in a controlled manner. A packer is attached to a wire line and introduced into the well. The weight of mud plus a pressure lock at the top of the well holds down the oil and gas. When the packer is installed at the bottom of the well, it includes a valve which is in a closed position. The wire line is retrieved and attached to a series of valves which are then introduced into the well. The first valve in the string is a sub-surface safety valve which is held closed by springs and well pressure. The only way to open that safety valve is to introduce a higher hydraulic pressure to override the springs and override the forces of well pressure. The safety valve must be closed when the well is swabbed.
One problem in connection with oil and gas wells is the presence of wet sour gas containing hydrogen sulfide (H.sub.2 S) and other corrosive fluids. H.sub.2 S is a colorless gas which is extremely dangerous if inhaled since the normal tolerance is two parts per million. In addition, H.sub.2 S is extremely corrosive since it forms sulfuric acid when combined with water. Hence, sealing is a severe problem. When H.sub.2 S is encountered during drilling, the normal procedure is to close the well permanently or burn it off.
Another problem associated with off shore drilling is the provision of a normally 20 foot radius in the well casing which must be traversed by the valve string. When traversing the 20 foot radius, seals on the periphery of the valve string can be damaged.
Another problem in connection with deep drilling is to provide seals which can withstand the temperature and pressures involved. For example, at a depth of 15,000 feet one frequently encounters temperatures of 400.degree. F. and pressures of 15,000 psi.
The present invention is directed to a solution of the above-mentioned sealing problems whereby a valve string may traverse a 20 foot radius in the well, will provide for controlled flow in hostile environments including H.sub.2 S, and has seals reliable at temperatures of 400.degree. F. and pressures of 15,000 psi. The solution to the H.sub.2 S problem will enable all previously closed wells to be activated.